Really old thread but I've been having this same problem with my S2 for a few months now, and have finally fixed it.Solution:
1. Make sure you've downloaded all the settings from http://www.2degreesmobile.co.nz/settings
onto your phone, ALL of them.
2. Go into the settings for internet (Settings->Wireless and network->Mobile Networks->Access Point Names->2degrees Internet) and DELETE the Proxy and Port values.
3. Power off your phone, remove the battery for 20 seconds, replace and power on.
That should do it. The tech (who also owns an S2 and develops for it) described it as an IP conflict between the internet and mms settings; apparently the 2degrees guys in charge of the settings files haven't gotten around to fixing them yet.
Worked for me after nothing else did... YMMV. Make sure Data Network is on and you're using data packets.